Polypropylene composition with improved impact resistance for pipe applications

ABSTRACT

The present invention relates to a polypropylene composition comprising a multimodal propylene random copolymer with at least one comonomer selected from alpha-olefins with 2 or 4 to 8 carbon atoms, wherein the polypropylene composition has a melt flow rate MFR 2  (2.16 kg, 230° C.) of 0.05 to 1.0 g/10 min, determined according to ISO 1133, a polydispersity index (PI) of 2.0 to 7.0, and a Charpy Notched Impact Strength at 0° C. of more than 4.0 kJ/m 2 , determined according to ISO 179/1eA:2000 using notched injection moulded specimens, a process for producing said polypropylene composition, an article comprising said polypropylene composition and the use of said polypropylene composition for the production of an article.

The present invention relates to propylene random copolymer compositionswith an improved balance of properties in regard of mechanicalproperties including impact properties and processing properties whichare suitable for pipe applications.

Polypropylene materials are frequently used for various pipe and pipefitting applications, such as fluid transport, e.g. water or naturalgas, during which the fluid is pressurized and/or heated. In particular,polypropylene materials are used in applications for plumbing andheating, such as in-house hot and cold water pressure pipes andfittings, floor and wall heating systems and radiator connections.

Thereby, propylene random copolymers are especially suitable forpressure pipe applications for hot water and industrial pipes as therandom copolymers have inter alia good impact performance, stiffness,creep resistance and slow crack properties and long term pressureresistance.

The expression “pressure pipe” used herein refers to a pipe which, whenused, is subjected to a positive pressure, that is the pressure insidethe pipe being higher than the pressure outside the pipe.

It is well known that increasing one of the impact or stiffnessproperties sacrifices the other.

Naturally, processability like extrusion output rate during pipeproduction and shorter cycle time during injection moulding of fittingsshould be industrially feasible, as well as the surface quality of thefinal pipe and/or fitting.

WO0068315 (EP1183307) discloses BNT nucleated homo polymer andheterophasic copolymer of propylene and the use thereof in variousapplication mainly concerned with moulding applications. The high meltflow rates of the compositions do not enable pipe applications.

WO 99/24479 of Borealis discloses nucleated propylene polymer, howeverexamples disclose homo polymers of propylene and heterophasic copolymersof propylene. The heterophasic copolymers of propylene are stated to be“stiff” (examples 9 and 10, e.g. flexural modulus of around 1500 and1600 MPa), whereby they are suitable for sewage pipe applications.

There is still a need for polypropylene copolymer compositions with animproved balance of impact and mechanical properties and good processingproperties which are suitable for pipe and pipe fittings and especiallyfor pressure pipe applications.

The present invention relates to a polypropylene composition suitablefor pipe applications comprising

a propylene random copolymer with at least one comonomer selected fromalpha-olefins with 2 or 4 to 8 carbon atoms

wherein the polypropylene composition has a melt flow rate MFR₂ (2.16kg, 230° C.) of 0.05 to 1.0 g/10 min, determined according to ISO 1133,a polydispersity index (PI) of 2.0 to 7.0, and a Charpy Notched ImpactStrength at 0° C. of at least 4.0 kJ/m², determined according to ISO179/1eA:2000 using notched injection moulded specimens.

The present invention is further characterized in that the multimodalpropylene random copolymer of the polypropylene composition of theinvention does not contain an elastomeric phase dispersed therein.

It has surprisingly been found that the polypropylene compositionaccording to the present invention has an advantageous property balancebetween mechanical properties in view of the Flexural Modulus and impactproperties, as can be seen from the Charpy Notched Impact Strength atcold temperature 0° C. and preferably also at room temperature. Thebalance between the Flexural Modulus and the Charpy Notched ImpactStrength at cold temperature provides sufficient flexibility and goodimpact properties to the polypropylene composition of the inventionmaking it highly suitable for pipe applications, more preferably for hotand cold water pressure pipe applications. More preferably the presentinventive polypropylene composition shows advantageously feasible creepresistance as can be seen from tensile stress. Further preferably, thepresent multimodal polypropylene composition has advantageous pressureresistance required for pressure pipe applications. The presentmultimodal polypropylene composition has preferably also an advantageousprocessing behavior in terms of pipe extrusion and/or cycle time ofmolded fittings. The obtained final pipe or fitting has a uniformshrinkage behavior and a good surface quality.

Pressure pipe for hot and cold water applications has a well-knownmeaning in the field of polypropylene pipe applications and implies fora skilled person generally accepted property requirements for the pipeto be usable in such applications.

A propylene random copolymer denotes a copolymer of propylene monomerunits and comonomer units in which the comonomer units are randomlydistributed in the polymeric chain. Thereby, a propylene randomcopolymer includes a fraction, which is insoluble in xylene-xylene coldinsoluble (XCU) fraction, in an amount of at least 70 wt %, morepreferably of at least 80 wt %, still more preferably of at least 85 wt% and most preferably of at least 90 wt %, based on the total amount ofthe propylene random copolymer.

The random copolymer does not contain an elastomeric polymer phasedispersed therein.

As known for skilled person, random copolymer is different fromheterophasic polypropylene which is a propylene copolymer comprising apropylene homo or random copolymer matrix component (1) and anelastomeric copolymer component (2) of propylene with one or more ofethylene and C4-C8 alpha-olefin copolymers, wherein the elastomeric(amorphous) copolymer component (2) is dispersed in said propylene homoor random copolymer matrix polymer (1).

Usually, a propylene polymer comprising at least two propylene polymerfractions (components), which have been produced under differentpolymerisation conditions resulting in different (weight average)molecular weights and/or different comonomer contents for the fractions,preferably produced by polymerizing in multiple polymerization stageswith different polymerization conditions, is referred to as“multimodal”. The prefix “multi” relates to the number of differentpolymer fractions the propylene polymer is consisting of. As an exampleof multimodal polypropylene, a propylene polymer consisting of twofractions only is called “bimodal”, whereas a propylene polymerconsisting of three fractions only is called “trimodal”.

Thereby the term “different” means that the propylene polymer fractionsdiffer from each other in at least one property, preferably in theweight average molecular weight or comonomer content or both, morepreferably at least in the weight average molecular weight.

The form of the molecular weight distribution curve, i.e. the appearanceof the graph of the polymer weight fraction as function of its molecularweight, of such a multimodal propylene polymer is at least distinctlybroadened in comparison with the curves for the individual fractions.

The propylene random copolymer used in the present invention ispreferably a multimodal propylene random copolymer, more preferably abimodal propylene random copolymer. Preferably, the propylene randomcopolymer consists of the two propylene copolymer fractions with theproviso that at least one of the two fractions, preferably bothfractions are propylene random copolymer fractions.

A propylene homopolymer thereby denotes a polymer consisting essentiallyof propylene monomer units. Due to the requirements of large-scalepolymerization it may be possible that the propylene homopolymerincludes minor amounts of comonomer units, which usually is below 0.1mol %, preferably below 0.05 mol %, most preferably below 0.01 mol % ofthe propylene homopolymer.

The propylene random copolymer used in the polypropylene composition ofthe invention comprises at least one comonomer selected fromalpha-olefins with 2 or 4 to 8 carbon atoms.

The propylene random copolymer may comprise only one type of comonomersor two or more types of comonomers.

The comonomers of said propylene random copolymer are preferablyselected from C₂ and C₄ to C₆ alpha-olefins. A particular preferredcomonomer is ethylene.

Especially suitable for the polypropylene composition of the presentinvention is a propylene random copolymer which is a propylene randomcopolymer with ethylene comonomer.

It is preferred that the propylene random copolymer, which is preferablythe propylene copolymer with ethylene comonomer, comprises at least apropylene random copolymer having a low molecular weight (low molecularweight (LMW) fraction) and a propylene random copolymer having a highmolecular weight (high molecular weight (HMW) fraction). Thereby, theLMW fraction has a lower weight average molecular weight than the HMWfraction.

It is well known that melt flow rate (MFR) of a polymer is an indicationof the weight average molecular weight (Mw) of the polymer, the higherthe MFR the lower the Mw of the polymer and, respectively, the lower theMFR the higher the Mw of the polymer. Accordingly, the MFR of the lowmolecular weight fraction is higher than the MFR of the high molecularweight fraction. The low molecular weight fraction has preferably a MFR₂of from 0.2 to 3.0 g/10 min, more preferably a MFR₂ from 0.25 to 2.0g/10 min, more preferably from 0.3 to 2.0 g/10 min and most preferablyof 0.35 to 2.0 g/10 min.

Preferably both the low molecular weight fraction and the high molecularweight fraction are propylene random copolymer fractions which may haveessentially the same or different comonomer content. It is preferredthat the comonomer content of the high molecular weight fraction isequal to or higher than, preferably higher than the comonomer content ofthe low molecular weight fraction.

The comonomer content of the low molecular weight fraction is usually inthe range of 1.0 to 6.0 mol %, preferably 2.0 to 5.5 mol %, morepreferably 3.0 to 5.0 mol %, most preferably 3.5 to 4.5 mol %, based onthe total content of monomeric units in the low molecular weightfraction.

The comonomer content of the high molecular weight fraction is usuallyin the range of 5.5 to 12 mol %, preferably 6.0 to 11.0 mol %, morepreferably 6.5 to 10.0 mol %%, still more preferably 7.0 to 9.0 mol %,most preferably 7.5 to 8.5 mol %, based on the total content ofmonomeric units in the high molecular weight fraction.

In a preferred embodiment of the invention, the propylene randomcopolymer is a propylene random copolymer with ethylene comonomercomprising at least a propylene random copolymer having a low molecularweight (low molecular weight (LMW) fraction) and a propylene randomcopolymer having a high molecular weight (high molecular weight (HMW)fraction) and a higher content of comonomer, preferably ethylenecomonomer, than the low molecular weight fraction (LMW fraction). Inthis preferred embodiment the content of the comonomer, preferablyethylene comonomer in the LMW fraction, is within the preferred rangesas defined above.

The comonomer content of the propylene random copolymer is usually inthe range of 4.5 to 9.5 mol %, preferably 5.0 to 9.0 mol %, morepreferably 5.5 to 8.0 mol %, still more preferably 5.5 to 7.5 mol %,most preferably 5.7 to 7.0 mol %, based on the total content ofmonomeric units in the propylene random copolymer.

The low molecular weight fraction and the high molecular weight fractionmay include the same type of comonomer or different types of comonomers.It is preferred that both fractions include the same type of comonomer.

The low molecular weight fraction is preferably present in the propylenerandom copolymer in an amount of 30 to 50 wt %, more preferably in anamount of 35 to 47 wt % and most preferably in an amount of 37 to 47 wt%, based on the total amount of the propylene random copolymer (100 wt%), preferably, and the high molecular weight fraction is preferablypresent in the propylene random copolymer in an amount of 70 to 50 wt %,more preferably in an amount of 65 to 53 wt % and most preferably in anamount of 63 to 53 wt %, based on the total amount of the propylenerandom copolymer (100 wt %).

The propylene random copolymer preferably has a density of 890 to 910kg/m³, preferably 895 to 905 kg/m³.

It is preferred that the propylene random copolymer consists of thepropylene random copolymer having a low molecular weight (low molecularweight (LMW) fraction), the propylene random copolymer having a highmolecular weight (high molecular weight (HMW) fraction), and optionalfurther additives, as defined above or below.

The multimodal propylene random copolymer may further comprise aprepolymer fraction. In case of the presence of a prepolymer fraction,said fraction is calculated to the amount (wt %) of the low molecularweight fraction or high molecular weight fraction, preferably to theamount of low molecular weight fraction. The prepolymer fraction can bepropylene homopolymer or copolymer.

It is especially preferred that polypropylene composition according tothe invention consists of the propylene random copolymer and optionalfurther additives, as defined above or below.

The amount of the propylene random copolymer is preferably 90.0 to 99.75wt %, more preferably of 95.0 to 99.75 wt % and even more preferably of96.5 to 99.75 wt %, based on the total weight of the polypropylenecomposition (100 wt %).

The polypropylene composition may in addition to the propylene randomcopolymer as described above further comprise other polymericcomponents. These polymeric components preferably are polyolefins, morepreferably are propylene homo- or copolymers. These additional polymerscan be present in the composition in an amount of up to 15 wt % of thetotal weight of the polypropylene composition (100 wt %).

However, it is preferred that the polymeric component of thepolypropylene composition consists of the propylene random copolymer asdefined above.

Moreover, the polypropylene composition of the invention may containadditives including without limiting to, clarifiers, brighteners, acidscavengers and antioxidants, as well as slip agents, inorganic fillerand UV light stabilizers. Each additive can be used e.g. in conventionalamounts, the total amount of additives present in the polypropylenecomposition being preferably as defined below. Such additives aregenerally commercially available and are described, for example, in“Plastic Additives Handbook”, 5th edition, 2001 of Hans Zweifel.

It is preferred that the polypropylene composition does not comprise apolymeric nucleating agent that is added on purpose to function as anucleating agent. More preferably, the polypropylene composition doesnot comprise (i.e. is void of) a polymeric nucleating agent, selectedfrom a polymerized vinyl compound according to the following formula

CH₂═CH—CHR¹R²  (I)

wherein R¹ and R² together form a 5- or 6-membered saturated,unsaturated or aromatic ring, optionally containing substituents, orindependently represent an alkyl group comprising 1 to 4 carbon atoms,whereby in case R¹ and R² form an aromatic ring, the hydrogen atom ofthe —CHR¹R² moiety is not present, for example vinyl cyclohexane (VCH)polymer.

The total amount of optional further additives is preferably between0.0001 and 2.5 wt %, more preferably between 0.0001 and 1.5 wt %, stillmore preferably between 0.0001 and 1.0 wt %, based on the total weightof the polypropylene composition (100 wt %). In case the optionaladditive(s) is added in an optional masterbatch, then the carriermaterial, e.g. carrier polymer, of the additive is calculated to the(total) amount of the additive(s), based on the total weight of thepolypropylene composition (100 wt %).

The polypropylene composition preferably has a melt flow rate MFR₂ (2.16kg, 230° C.) of from 0.1 to 1.0 g/10 min, preferably of from 0.1 to 0.7g/10 min, more preferably of from 0.15 to 0.5 g/10 min, most preferablyof from 0.2 to 0.4 g/10 min, determined according to ISO 1133.

The polypropylene composition additionally has a polydispersity index PIof from 2.0 to 7.0, preferably from 2.0 to 6.0, preferably of from 2.5to 5.0, more preferably of from 2.7 to 4.5 and most preferably of from2.7 to 4.0. The polydispersity index is determined from rheologicalmeasurements as described below in the example section.

Further, the polypropylene composition preferably has a content ofxylene cold solubles (XCS) of from 1.0 to 15.0 wt %, preferably of from2.0 to 12.0 wt %, more preferably of from 4.0 to 10.0 wt %, determinedat 25° C. according to ISO 16152.

The polypropylene composition preferably has a Charpy Notched ImpactStrength at 0° C. of at least 5.0 kJ/m², more preferably of at least 6.0kJ/m², still more preferably of at least 6.5 kJ/m², determined accordingto ISO 179/1eA:2000 using notched injection moulded specimens. The upperlimit of the Charpy Notched Impact Strength at 0° C. is preferably nothigher than 15 kJ/m2.

Also preferably, the polypropylene composition has a Charpy NotchedImpact Strength at 23° C. of at least 30 kJ/m², preferably of at least40 kJ/m², more preferably of at least 45 kJ/m², determined according toISO 179/1eA:2000 using notched injection moulded specimens. The upperlimit of the Charpy Notched Impact Strength at 23° C. is preferably nothigher than 100 kJ/m².

The polypropylene composition preferably has a flexural modulus at least700 MPa, preferably at least 750 MPa, most preferably at least 780 MPa,determined according to ISO 178 at a test speed of 2 mm/min and a forceof 100N on test specimens having a dimension of 80×10×4.0 mm³(length×width×thickness) prepared by injection moulding according to ENISO 1873-2. The upper limit of the flexural modulus usually does notexceed 1400 MPa, and is preferably 1200 MPa or less. The polypropylenecomposition most preferably has a flexural modulus of 780 to 1100 MPa.

Further, the polypropylene composition preferably has a tensile stressat yield of at least 15 MPa, more preferably at least 20 MPa, mostpreferably at least 23 MPa, determined according to ISO 527-2:1996 usingtype 1A injection moulded test specimens prepared according to ISO527-2:1996. The upper limit of the tensile stress at yield usually doesnot exceed 50 MPa and is preferably not higher than 45 MPa.

The shrinkage of the polypropylene composition after forming thecomposition into an article, preferably a pipe or a pipe fitting, ispreferably not more than 6%, more preferably not more than 5%, mostpreferably not more than 4%.

The polypropylene composition of the invention is preferably produced ina continuous multistage process in a conventional manner. It is to beunderstood that as soon as the inventors have found the advantageousproperty balance resulting to the polypropylene composition, then forindustrial scale production it is within the skills of a skilled personto adjust process parameters and controls to obtain the properties ofthe polypropylene composition. The process preferably comprises at leasttwo polymerisation stages.

Accordingly a process for producing a polypropylene composition asdescribed above or below, wherein the propylene random copolymer ispolymerized in a multistage polymerization process in the presence of

-   -   (I) a solid catalyst component comprising a magnesium halide, a        titanium halide and an internal electron donor; and    -   (II) a cocatalyst comprising an aluminium alkyl and optionally        an external electron donor,        the multistage process comprising the steps of    -   (a) continuously polymerizing propylene together with a        comonomer selected from alpha-olefins with 2 or 4 to 8 carbon        atoms, in a first polymerization stage by introducing streams of        propylene, hydrogen and said comonomer into the first        polymerization stage at a temperature of 60 to 80° C. and a        pressure of 3000 to 6500 kPa to produce a first propylene random        copolymer, wherein said first propylene random copolymer has a        melt flow rate MFR₂ (2.16 kg; 230° C.; ISO 1133) of from 0.2 to        3.0 g/min;    -   (b) withdrawing from the first polymerization stage a stream        comprising said first propylene random copolymer and        transferring said stream into a second polymerization stage;    -   (c) polymerizing propylene together with a comonomer selected        from alpha-olefins with 2 or 4 to 8 carbon atoms, in said second        polymerization stage by introducing streams of propylene, said        comonomer and optionally hydrogen into said second        polymerization stage at a temperature of 70 to 90° C. and a        pressure of 1000 to 3000 kPa to produce a propylene random        copolymer of said first propylene random copolymer and a second        propylene random copolymer;    -   (d) continuously withdrawing a stream comprising said propylene        random copolymer from the second polymerization stage and        optionally mixing said propylene random copolymer with        additives; and    -   (e) extruding said propylene random copolymer mixture into        pellets, which have a melt flow rate MFR₂ (2.16 kg; 230° C.;        ISO 1133) of from 0.05 to 1.0 g/min,    -   and wherein the first propylene random copolymer has preferably        a a higher MFR₂ than the second propylene random copolymer.

The process of the invention is described in further details below:

Thereby, conventional polymerization techniques, e.g. gas phase,solution phase, slurry or bulk polymerization can be used.

In general, a combination of slurry (or bulk) and at least one gas phasereactor is often preferred for the polymerisation of the propylenerandom copolymer. It is further preferred that the reactor order isslurry (or bulk) then one or more gas phase reactors.

In case of propylene polymerisation for slurry reactors, the reactiontemperature will generally be in the range 60 to 110° C., e.g. 60 to 85°C., the reactor pressure will generally be in the range 5 to 80 bar,e.g. 20 to 60 bar, and the residence time will generally be in the range0.1 to 5 hours, e.g. 0.3 to 2 hours. The monomer is usually used asreaction medium.

For gas phase reactors, the reaction temperature used will generally bein the range 60 to 115° C., e.g. 70 to 110° C., the reactor pressurewill generally be in the range 10 to 25 bar, and the residence time willgenerally be 0.5 to 8 hours, e.g. 0.5 to 4 hours. The gas used will bethe monomer optionally as mixture with a non-reactive gas such asnitrogen or propane.

In addition to actual polymerisation steps and reactors, the process cancontain any additional polymerisation steps, like prepolymerisationstep, and any further after reactor handling steps as known in the art.

It is preferred that the propylene random copolymer is produced in asequential polymerization process comprising at least two polymerizationzones operating at different conditions to produce the propylene randomcopolymer. The polymerization zones may operate in slurry, solution, orgas phase conditions or their combinations. Suitable processes aredisclosed, among others, in WO-A-98/58975, WO-A-98/58976, EP-A-887380and WO-A-98/58977.

In a preferred embodiment, the prepolymerization is conducted in acontinuous manner as bulk slurry polymerization in liquid propylene,i.e. the liquid phase mainly comprises propylene, with minor amount ofother reactants and optionally inert components dissolved therein.Preferably the prepolymerization is conducted in a continuous stirredtank reactor or a loop reactor, preferably in a loop reactor.

The prepolymerization reaction is typically conducted at a temperatureof 0 to 60° C., preferably from 10 to 50° C., and more preferably from20 to 45° C.

The pressure in the prepolymerization reactor is not critical but mustbe sufficiently high to maintain the reaction mixture in liquid phase.Thus, the pressure may be from 20 to 100 bar, for example 30 to 70 bar.

The reaction conditions are well known in the art as disclosed, amongothers, in GB 1580635.

In the prepolymerization step it is also possible to feed comonomersinto the prepolymerization stage. Examples of suitable comonomers areethylene or alpha-olefins having from 4 to 8 carbon atoms. Especiallysuitable comonomers are ethylene, 1-butene, 1-hexene, 1-octene or theirmixtures. Especially preferred is ethylene as comonomer.

In a preferred embodiment for polymerizing the propylene randomcopolymer the first propylene random copolymer is preferably produced ina first polymerization stage.

Said first propylene random copolymer most preferably reflects the lowmolecular weight (LMW) fraction of the propylene random copolymer asdefined above.

The first propylene random copolymer is produced by introducing apolymerization catalyst, optionally through the prepolymerization stageas disclosed above, into the first polymerization stage together with afirst monomer mixture containing propylene and a comonomer selected fromethylene and alpha-olefins containing 4 to 8 carbon atoms. The contentof the comonomers is controlled to obtain a desired comonomer content inthe first propylene random copolymer. The comonomer content of saidfirst propylene random copolymer preferably reflects the comonomercontent of the low molecular weight (LMW) fraction of the propylenerandom copolymer as defined above.

The first propylene random copolymer produced in the firstpolymerization stage has a MFR₂ of from 0.2 to 3.0 g/10 min. Preferablythe MFR₂ of the first propylene random copolymer, preferably of the lowmolecular weight (LMW) fraction of the propylene random copolymer, isfrom 0.25 to 2.0 g/10 min, more preferably from 0.3 to 2.0 g/10 min andmost preferably of 0.35 to 2.0 g/10 min.

The polymerization in the first polymerization zone is preferablyconducted in slurry in a loop reactor. For this reason the terms “firstpolymerization stage” and “loop reactor” may be used interchangeablywithin the context of the present invention. Then the polymer particlesformed in the polymerization, together with the catalyst fragmented anddispersed within the particles, are suspended in the fluid hydrocarbon.The slurry is agitated to enable the transfer of reactants from thefluid into the particles. In loop reactors the slurry is circulated witha high velocity along a closed pipe by using a circulation pump. Loopreactors are generally known in the art and examples are given, forinstance, in U.S. Pat. No. 4,582,816, US-A-3405109, U.S. Pat. No.3,324,093, EP-A-479186 and U.S. Pat. No. 5,391,654.

Slurry polymerization is preferably a so called bulk polymerization. By“bulk polymerization” is meant a process where the polymerization isconducted in a liquid monomer essentially in the absence of an inertdiluent. However, as it is known to a person skilled in the art themonomers used in commercial production are never pure but always containaliphatic hydrocarbons as impurities. For instance, the propylenemonomer may contain up to 5% of propane as an impurity. As propylene isconsumed in the reaction and also recycled from the reaction effluentback to the polymerization, the inert components tend to accumulate, andthus the reaction medium may comprise up to 40 wt-% of other compoundsthan monomer. It is to be understood, however, that such apolymerization process is still within the meaning of “bulkpolymerization”, as defined above.

The temperature in the slurry polymerization is typically from 50 to110° C., preferably from 60 to 80° C. and more preferably from 65 to 75°C. The pressure is from 1 to 150 bar, preferably from 10 to 100 bar andmost preferably from 30 to 65 bar.

The slurry may be withdrawn from the reactor either continuously orintermittently. A preferred way of intermittent withdrawal is the use ofsettling legs where the solids concentration of the slurry is allowed toincrease before withdrawing a batch of the concentrated slurry from thereactor. The use of settling legs is disclosed, among others, inUS-A-3374211, U.S. Pat. No. 3,242,150 and EP-A-1310295. Continuouswithdrawal is disclosed, among others, in EP-A-891990, EP-A-1415999,EP-A-1591460 and EP-A-1860125. The continuous withdrawal may be combinedwith a suitable concentration method, as disclosed in EP-A-1860125 andEP-A-1591460.

Into the slurry polymerization stage other components are alsointroduced as it is known in the art. Thus, hydrogen is used to controlthe molecular weight of the polymer. Process additives, such asantistatic agent, may be introduced into the reactor to facilitate astable operation of the process.

Preferably, the ratio of comonomer to propylene in the firstpolymerization stage is in the range of 0.2 to 20 mol/kmol, morepreferably in the range of 0.5 to 15 mol/kmol, still more preferably inthe range of 0.5 to 10 mol/kmol and most preferably in the range of 1 to10 mol/kmol.

Preferably, the ratio of hydrogen to propylene in the firstpolymerization stage is in the range of 0.1 to 5.0 mol/kmol, morepreferably in the range of 0.1 to 2.5 mol/kmol, still more preferably inthe range of 0.2 to 1.5 mol/kmol and most preferably in the range of 0.3to 1.0 mol/kmol.

The slurry is preferably conducted directly into a second polymerizationstage, which preferably is a gas phase polymerization stage, to producethe second propylene random copolymer. By “directly” it is meant thatthe slurry is introduced from the loop reactor into the gas phasereactor without a flash step between the slurry and gas phasepolymerization stages for removing at least a part of the reactionmixture from the polymer. Thereby, substantially the entire slurrystream withdrawn from the first polymerization stage is directed to thesecond polymerization stage. This kind of direct feed is described inEP-A-887379, EP-A-887380, EP-A-887381 and EP-A-991684. It is preferredthat the whole slurry stream withdrawn from the loop reactor is directedinto the gas phase reactor without any separation step in between.However, it is within the scope of the present invention to take smallsamples or sample streams from the polymer or from the fluid phase orfrom both for analyzing the polymer and/or the composition of thereaction mixture. As understood by the person skilled in the art, thevolume of such sample streams is small compared to the total slurrystream withdrawn from the loop reactor and typically much lower than 1%by weight of the total stream, such as at most 0.1% or 0.01% or even0.001% by weight.

When the entire slurry stream from the first polymerization stage isintroduced into the second polymerization stage then substantial amountsof propylene, comonomer and hydrogen are introduced into the secondpolymerization stage together with the polymer.

As discussed above, a certain amount of propylene and comonomer isintroduced into the second polymerization stage from the firstpolymerization stage. However, this is generally not sufficient tomaintain desired propylene and comonomer concentrations in the secondpolymerization stage. Therefore additional propylene and comonomer aretypically introduced into the second polymerization stage. They areintroduced to maintain a desired propylene concentration and to reach adesired ratio of comonomer to propylene in the fluidization gas. Eventhough the actual comonomer to monomer ratio that is needed to reach thedesired content of comonomer in the polymer depends on the catalyst usedin the process, the composition of the monomer and comonomer feeds issuitably adjusted so that the fluidization gas has a ratio of comonomerto propylene of about 10 to 100 mol/kmol, preferably from 15 to 70mol/kmol. Such ratios have been found to yield good results for somecatalysts.

It is also often necessary to introduce additional hydrogen into thesecond polymerization stage to control the MFR of the copolymer mixture.Suitably, the hydrogen feed is controlled to maintain constant hydrogento propylene ratio in the fluidization gas. The actual ratio depends onthe catalyst. Good results have been obtained by maintaining the ratiowithin the range of from 0.1 to 3 mol/kmol, preferably from 0.2 to 2mol/kmol.

In a fluidized bed gas phase reactor olefins are polymerized in thepresence of a polymerization catalyst in an upwards moving gas stream.The reactor typically contains a fluidized bed comprising the growingpolymer particles containing the active catalyst, said fluidized bedhaving its base above a fluidization grid.

The polymer bed is fluidized with the help of the fluidization gascomprising the olefin monomer, eventual comonomer(s), eventual chaingrowth controllers or chain transfer agents, such as hydrogen, andeventual inert gas. The fluidization gas is introduced into an inletchamber at the bottom of the reactor. To make sure that the gas flow isuniformly distributed over the cross-sectional surface area of the inletchamber the inlet pipe may be equipped with a flow dividing element asknown in the art, e.g. U.S. Pat. No. 4,933,149 and EP-A-684871. One ormore of the above-mentioned components may be continuously added intothe fluidization gas to compensate for losses caused, among other, byreaction or product withdrawal.

From the inlet chamber the gas flow is passed upwards through afluidization grid into the fluidized bed. The purpose of thefluidization grid is to divide the gas flow evenly through thecross-sectional area of the bed. Sometimes the fluidization grid may bearranged to establish a gas stream to sweep along the reactor walls, asdisclosed in WO-A-2005/087361. Other types of fluidization grids aredisclosed, among others, in U.S. Pat. No. 4,578,879, EP 600414 andEP-A-721798. An overview is given in Geldart and Bayens: The Design ofDistributors for Gas-fluidized Beds, Powder Technology, Vol. 42, 1985.

The fluidization gas passes through the fluidized bed. The superficialvelocity of the fluidization gas must be higher that minimumfluidization velocity of the particles contained in the fluidized bed,as otherwise no fluidization would occur. On the other hand, thevelocity of the gas should be lower than the terminal velocity, asotherwise the whole bed would be entrained with the fluidization gas.The minimum fluidization velocity and the terminal velocity can becalculated when the particle characteristics are known by using commonengineering practise. An overview is given, among others in Geldart: GasFluidization Technology, J. Wiley & Sons, 1986.

When the fluidization gas is contacted with the bed containing theactive catalyst the reactive components of the gas, such as monomers andchain transfer agents, react in the presence of the catalyst to producethe polymer product. At the same time the gas is heated by the reactionheat.

The unreacted fluidization gas is removed from the top of the reactorand cooled in a heat exchanger to remove the heat of reaction. The gasis cooled to a temperature which is lower than that of the bed toprevent the bed from heating because of the reaction. It is possible tocool the gas to a temperature where a part of it condenses. When theliquid droplets enter the reaction zone they are vaporised. Thevaporisation heat then contributes to the removal of the reaction heat.This kind of operation is called condensed mode and variations of it aredisclosed, among others, in WO-A-2007/025640, U.S. Pat. No. 4,543,399,EP-A-699213 and WO-A-94/25495. It is also possible to add condensingagents into the recycle gas stream, as disclosed in EP-A-696293. Thecondensing agents are non-polymerizable components, such as n-pentane,isopentane, n-butane or isobutane, which are at least partiallycondensed in the cooler.

The gas is then compressed and recycled into the inlet chamber of thereactor. Prior to the entry into the reactor fresh reactants areintroduced into the fluidization gas stream to compensate for the lossescaused by the reaction and product withdrawal. It is generally known toanalyze the composition of the fluidization gas and introduce the gascomponents to keep the composition constant. The actual composition isdetermined by the desired properties of the product and the catalystused in the polymerization.

The polymeric product may be withdrawn from the gas phase reactor eithercontinuously or intermittently. Combinations of these methods may alsobe used. Continuous withdrawal is disclosed, among others, inWO-A-00/29452. Intermittent withdrawal is disclosed, among others, inUS-A-4621952, EP-A-188125, EP-A-250169 and EP-A-579426.

The top part of the gas phase reactor may include a so calleddisengagement zone. In such a zone the diameter of the reactor isincreased to reduce the gas velocity and allow the particles that arecarried from the bed with the fluidization gas to settle back to thebed.

The bed level may be observed by different techniques known in the art.For instance, the pressure difference between the bottom of the reactorand a specific height of the bed may be recorded over the whole lengthof the reactor and the bed level may be calculated based on the pressuredifference values. Such a calculation yields a time-averaged level. Itis also possible to use ultrasonic sensors or radioactive sensors. Withthese methods instantaneous levels may be obtained, which of course maythen be averaged over time to obtain a time-averaged bed level.

Also antistatic agent(s) may be introduced into the gas phase reactor ifneeded. Suitable antistatic agents and methods to use them aredisclosed, among others, in U.S. Pat. No. 5,026,795, U.S. Pat. No.4,803,251, U.S. Pat. No. 4,532,311, U.S. Pat. No. 4,855,370 andEP-A-560035. They are usually polar compounds and include, among others,water, ketones, aldehydes and alcohols.

The reactor may also include a mechanical agitator to further facilitatemixing within the fluidized bed. An example of suitable agitator designis given in EP-A-707513.

Typically the fluidized bed polymerization reactor is operated at atemperature within the range of from 50 to 100° C., preferably from 70to 90° C. The pressure is suitably from 10 to 40 bar, preferably from 10to 30 bar.

In the second polymerization stage preferably a copolymer mixturecomprising the first propylene random copolymer and a second copolymeris formed.

Said first propylene random copolymer preferably reflects the propylenerandom copolymer having a low molecular weight (LMW) fraction of thepropylene random copolymer and said second propylene random copolymerpreferably reflects the high molecular weight (HMW) fraction of thepropylene random copolymer as defined above. Thus, copolymer mixturecomprising the first propylene random copolymer and a second propylenerandom copolymer preferably reflects a mixture of the low molecularweight (LMW) fraction and the high molecular weight (HMW) fraction ofthe propylene random copolymer as defined above. The amount of anyprepolymer fraction thereby preferably adds to the amount of the lowmolecular weight fraction.

The copolymer mixture is formed by introducing the particles of thefirst propylene random copolymer, containing active catalyst dispersedtherein, together with additional propylene and comonomer into thesecond polymerization stage. This causes the second copolymer to form onthe particles containing the first propylene random copolymer. Thesecond polymerization stage is preferably conducted in a fluidized bedgas phase reactor. For this reason the terms “second polymerizationstage” and “gas phase reactor” may be used interchangeably within thecontext of the present invention.

The comonomer is selected from ethylene and alpha-olefins containing 4to 8 carbon atoms. The comonomer used in the second polymerization stagemay be the same as or different from the comonomer used in the firstpolymerization stage. Preferably the same comonomer is used in the firstand the second polymerization stages.

Also in the second polymerization stage the content of the comonomers iscontrolled to obtain the desired comonomer content of the copolymermixture. The obtained reaction mixture is the polymer of propylenerandom copolymer.

Typically the obtained propylene random copolymer contains from 4.5 to9.5 mol % units derived from the comonomer.

Furthermore, the comonomer content of the obtained propylene randomcopolymer is equal to or higher than the comonomer content of the firstpropylene random copolymer. Preferably the ratio of the comonomercontent of the first propylene random copolymer to the comonomer contentof the obtained propylene random copolymer (both expressed in mol %),C₁/C_(b), is not higher than 0.9, more preferably not higher than 0.8,especially preferably not higher than 0.7.

The MFR₂ of the obtained propylene random copolymer is from 0.05 to 1.0g/10 min. Preferably the MFR₂ of the obtained propylene random copolymeris from 0.1 to 0.7 g/10 min. Furthermore, the MFR of the obtainedpropylene random copolymer is lower than the MFR of the first propylenerandom copolymer. Preferably, the ratio of the MFR of the obtainedpropylene random copolymer to MFR of the first propylene randomcopolymer, MFR_(2,b)/MFR_(2,1), has a value of not higher than 0.8, morepreferably not higher than 0.6 and in particular not higher than 0.5.

According to a preferred embodiment of the invention the ratio C₁/C_(b)is not higher than 0.9 and the ratio MFR_(2,b)/MFR_(2,1) is not higherthan 0.8; more preferably the ratio C₁/C_(b) is not higher than 0.7 andthe ratio MFR_(2,b)/MFR_(2,1) is not higher than 0.5.

The obtained propylene random copolymer preferably comprises the ratioof the first propylene random copolymer to second random copolymer asdefined above or in claims.

As to catalyst, the propylene random copolymer can be produced bypolymerisation in the presence of any conventional coordination catalystincluding Ziegler-Natta, chromium and single site (like metallocenecatalyst), preferably in the presence of a Ziegler-Natta catalyst. SuchZiegler-Natta catalysts typically comprise a solid transition metalcomponent and a cocatalyst.

The solid Ziegler Natta catalyst component preferably comprises atransition metal component which preferably is a titanium halide and amagnesium halide. These compounds may be supported on a particulatesupport, such as inorganic oxide, like silica or alumina, or, usually,the magnesium halide to form above said solid support. Examples of suchsolid catalyst components are disclosed, among others, in WO 87/07620,WO 92/21705, WO 93/11165, WO 93/11166, WO 93/19100, WO 97/36939, WO98/12234, WO 99/33842.

As is well known, the solid catalyst components for polymerising thepropylene random copolymer typically comprise, in addition to themagnesium halide and transition metal compound, an electron donor(internal electron donor).

Suitable electron donors are, among others, esters of carboxylic acids,like phthalates, citraconates, and succinates. Also oxygen- ornitrogen-containing silicon compounds may be used. Examples of suitablecompounds are shown in WO 92/19659, WO 92/19653, WO 92/19658, U.S. Pat.No. 4,347,160, U.S. Pat. No. 4,382,019, U.S. Pat. No. 4,435,550, U.S.Pat. No. 4,465,782, U.S. Pat. No. 4,473,660, U.S. Pat. No. 4,530,912 andU.S. Pat. No. 4,560,671.

Moreover, said solid catalyst components are preferably used incombination with well known external electron donors, including withoutlimiting to, ethers, ketones, amines, alcohols, phenols, phosphines andsilanes, for example organosilane compounds containing Si—OCOR, Si—OR,or Si—NR₂ bonds, having silicon as the central atom, and R is an alkyl,alkenyl, aryl, arylalkyl or cycloalkyl with 1-20 carbon atoms; and wellknown cocatalysts, which preferably comprise an aluminium alkyl compoundas known in the art to polymerise the propylene random copolymer.

Extrusion:

When the polymer has been removed from the last polymerisation stage, itis preferably subjected to process steps for removing the residualhydrocarbons from the polymer. Such processes are well known in the artand can include pressure reduction steps, purging steps, strippingsteps, extraction steps and so on. Also combinations of different stepsare possible. After the removal of residual hydrocarbons the secondpropylene copolymer composition is preferably mixed with additives as itis well known in the art. Such additives include antioxidants, processstabilizers, neutralisers, lubricating agents, pigments and so on. Thepolymer particles are then extruded to pellets as it is known in theart. Preferably co-rotating twin screw extruder is used for theextrusion step. Such extruders are manufactured, for instance, byCoperion (Werner & Pfleiderer) and Japan Steel Works.

Article of the Invention:

Further, the present invention relates to an article comprising themultimodal polypropylene composition according to the present invention.

In a preferred embodiment, the article is selected from an extrudedarticle, preferably a pipe application, or a moulded article, preferablyan injection moulded or blow moulded article, application morepreferably a fitting for pipe applications, comprising the multimodalpolypropylene composition of the invention. The pipe and fittingproduced from the polypropylene composition according to the inventionpreferably has good mechanical properties as described above and shownbelow in experimental part. Thus, the pipe according to the inventionpreferably qualifies as pressure pipe.

Pipe of the invention can be

a monolayer pipe, wherein the pipe layer comprises, preferably consistsof, the multimodal polypropylene composition of the invention, or

-   -   a multilayer pipe, wherein at least one layer comprises,        preferably consists of, the multimodal polypropylene composition        of the invention.

The preferred pipe of the invention has at least one layer comprising,preferably consisting of, the multimodal polypropylene composition ofthe invention. Preferred pipe is a pressure pipe, more preferably apressure pipe for hot and cold water applications.

Fitting of the invention preferably consists of the multimodalpolypropylene composition of the invention.

Production of Pipe of the Invention:

Pipes can be produced from the multimodal polypropylene compositionaccording to the present invention according to the methods known in theart. Thus, according to one preferred method the multimodalpolypropylene composition is extruded through an annular die to adesired internal diameter, after which the multimodal polypropylenecomposition is cooled.

The pipe extruder preferably operates at a relatively low temperatureand therefore excessive heat build-up should be avoided. Extrudershaving a high length to diameter ratio L/D more than 15, preferably ofat least 20 and in particular of at least 25 are preferred. The modernextruders typically have an L/D ratio of from about 30 to 35.

The polymer melt is extruded through an annular die, which may bearranged either as end-fed or side-fed configuration. The side-fed diesare often mounted with their axis parallel to that of the extruder,requiring a right-angle turn in the connection to the extruder. Theadvantage of side-fed dies is that the mandrel can be extended throughthe die and this allows, for instance, easy access for cooling waterpiping to the mandrel.

After the plastic melt leaves the die it is calibrated to the correctdiameter. In one method the extrudate is directed into a metal tube(calibration sleeve). The inside of the extrudate is pressurised so thatthe plastic is pressed against the wall of the tube.

According to another method the extrudate leaving the die is directedinto a tube having a perforated section in the centre. A slight vacuumis drawn through the perforation to hold the pipe against the walls ofthe sizing chamber.

After the sizing the pipe is cooled, typically in a water bath having alength of about 5 metres or more.

Production of Fittings of the Invention:

Fittings of the invention can be produced from the multimodalpolypropylene composition according to the present invention using themethods and equipment known in the art. Thus, according to one preferredmethod the multimodal polypropylene composition is moulded, preferablyinjection moulded or blown moulded, more preferably injection moulded,in a conventional manner using conventional moulding equipment, to ashape of a fitting for a pipe.

EXAMPLES 1. Determination Methods

a) Melt Flow Rate

The melt flow rate (MFR) is determined according to ISO 1133 and isindicated in g/10 min. The MFR is an indication of the flowability, andhence the processability, of the polymer. The higher the melt flow rate,the lower the viscosity of the polymer. The MFR₂ of polypropylene at atemperature 230° C. and a load of 2.16 kg.

The MFR₂ is herein assumed to follow the following mixing rule (equation1):

$\begin{matrix}{{MI}_{b} = \left( {{w_{1}{MI}_{1}^{- 0.0965}} + {w_{2} \cdot {MI}_{2}^{- 0.0965}}} \right)^{- \frac{1}{0.0965\;}}} & \left( {{eq}.\mspace{14mu} 1} \right)\end{matrix}$

Where w is the weight fraction of the component in the mixture, MI isthe MFR₂ and subscripts b, 1 and 2 refer to the mixture, component 1 andcomponent 2, respectively.

b) Density

Density of the polymer was measured according to ISO 1183-1:2004 MethodA on compression moulded specimen prepared according to EN ISO1872-2(February 2007) and is given in kg/m³.

c) Comonomer Content

The comonomer content was determined by quantitative Fourier transforminfrared spectroscopy (FTIR) after basic assignment calibrated viaquantitative ¹³C nuclear magnetic resonance (NMR) spectroscopy in amanner well known in the art. Thin films are pressed to a thickness ofbetween 100-500 micrmeter and spectra recorded in transmission mode.

Specifically, the ethylene content of a polypropylene-co-ethylenecopolymer is determined using the baseline corrected peak area of thequantitative bands found at 720-722 and 730-733 cm⁻¹. Specifically, thebutene or hexene content of a polypropylene copolymer is determinedusing the baseline corrected peak area of the quantitative bands foundat 1377-1379 cm⁻¹. Quantitative results are obtained based uponreference to the film thickness.

The comonomer content is herein assumed to follow the mixing rule(equation 2):

C _(b) =w ₁ ·C ₁ +w ₂ ·C ₂  (eq. 2)

Where C is the content of comonomer in weight-%, w is the weightfraction of the component in the mixture and subscripts b, 1 and 2 referto the overall mixture, component 1 and component 2, respectively.

As it is well known to the person skilled in the art the comonomercontent in weight basis in a binary copolymer can be converted to thecomonomer content in mole basis by using the following equation

$\begin{matrix}{c_{m} = \frac{1}{1 + {\left( {\frac{1}{c_{w\;}} - 1} \right) \cdot \frac{M\; W_{\sigma}}{M\; W_{m}}}}} & \left( {{eq}.\mspace{14mu} 3} \right)\end{matrix}$

where c_(m) is the mole fraction of comonomer units in the copolymer,c_(w) is the weight fraction of comonomer units in the copolymer, MW_(c)is the molecular weight of the comonomer (such as ethylene) and MW_(m)is the molecular weight of the main monomer (i.e., propylene).

d) Xylene Cold Solubles

Xylene cold solubles (XCS, wt.-%) content was determined at 25° C.according ISO 16152; first edition; 2005-07-01.

The content of xylene soluble polymer is herein assumed to follow themixing rule (equation 4):

XS _(b) =w ₁ ·XS ₁ +w ₂ ·XS ₂  (eq. 4)

Where XS is the content of xylene soluble polymer in weight-%, w is theweight fraction of the component in the mixture and subscripts b, 1 and2 refer to the overall mixture, component 1 and component 2,respectively.

e) Flexural Modulus

The flexural modulus was determined according to ISO 178. The testspecimens having a dimension of 80×10×4.0 mm³ (length×width×thickness)were prepared by injection molding according to EN ISO 1873-2. Thelength of the span between the supports was 64 mm, the test speed was 2mm/min and the force was 100 N.

f) Tensile Stress at Yield, Tensile Strain at Yield

Tensile stress at yield and tensile strain at yield was determinedaccording to ISO 527-1:1996 and ISO 527-2:1996 on test specimen ISO527-2:1996 type 1A molded specimen, the Injection moulding carried outaccording to ISO 1873-2:2007.

g) Charpy Notched Impact Strength

Charpy notched impact strength (Charpy NIS) was determined according toISO 179-1:2000 on notched specimen of 80×10×4 mm, cut from test specimenISO 527-2:1996 type 1A. Notched impact specimen according to ISO179-1/1eA:2000 was used. Testing temperature is 23±2° C. for Charpy NISat 23° C. and 0±2° C. for Charpy NIS at 0° C. Injection moulding carriedout according to ISO 1873-2:2007.

h) Rheological Parameters, Polydispersity Index

The characterization of polymer melts by dynamic shear measurementscomplies with ISO standards 6721-1 and 6721-10. The measurements wereperformed on an Anton Paar MCR501 stress controlled rotationalrheometer, equipped with a 25 mm parallel plate geometry. Measurementswere undertaken on compression moulded plates, using nitrogen atmosphereand setting a strain within the linear viscoelastic regime. Theoscillatory shear tests were done at T 190° C. applying a frequencyrange between 0.01 and 600 rad/s and setting a gap of 1.3 mm.

In a dynamic shear experiment the probe is subjected to a homogeneousdeformation at a sinusoidal varying shear strain or shear stress (strainand stress controlled mode, respectively). On a controlled strainexperiment, the probe is subjected to a sinusoidal strain that can beexpressed by

γ(t)=γ₀ Sin(ωt)  (1)

If the applied strain is within the linear viscoelastic regime, theresulting sinusoidal stress response can be given by

σ(t)=σ₀ sin(ωt+δ)  (2)

where

σ₀ and γ₀ are the stress and strain amplitudes, respectively

ω is the angular frequency

δ is the phase shift (loss angle between applied strain and stressresponse)

t is the time

Dynamic test results are typically expressed by means of severaldifferent rheological functions, namely the shear storage modulus G′,the shear loss modulus, G″, the complex shear modulus, G*, the complexshear viscosity, η*, the dynamic shear viscosity, η′, the out-of-phasecomponent of the complex shear viscosity η″ and the loss tangent, tan δwhich can be expressed as follows:

$\begin{matrix}{G^{\prime} = {\frac{\sigma_{0}}{\gamma_{0}}\cos \; {\delta \lbrack{Pa}\rbrack}}} & (3) \\{G^{\prime} = {\frac{\sigma_{0}}{\gamma_{0}}\sin \; {\delta \lbrack{Pa}\rbrack}}} & (4) \\{G^{*} = {G^{\prime} + {{G}^{''}\lbrack{Pa}\rbrack}}} & (5) \\{\eta^{*} = {\eta^{\prime} - {\; {\eta^{''}\left\lbrack {{Pa}.s} \right\rbrack}}}} & (6) \\{\eta^{\prime} = {\frac{G^{''}}{\omega}\left\lbrack {{Pa}.s} \right\rbrack}} & (7) \\{\eta^{''} = {\frac{G^{\prime}}{\omega}\left\lbrack {{Pa}.s} \right\rbrack}} & (8)\end{matrix}$

The values of storage modulus (G′), loss modulus (G″), complex modulus(G*) and complex viscosity (η*) were obtained as a function of frequency(ω). Thereby, e.g. η_(0.05 rad/s) (eta*_(0.05 rad/s)) is used asabbreviation for the complex viscosity at the frequency of 0.05 rad/s.

The polydispersity index, PI, is defined by equation 9.

$\begin{matrix}{{{PI} = \frac{10^{5}}{G^{\prime}\left( \omega_{COP} \right)}},{\omega_{COP} = {\omega \mspace{14mu} {for}\mspace{14mu} \left( {G^{\prime} = G^{''}} \right)}}} & (9)\end{matrix}$

where, ω_(COP) is the cross-over angular frequency, determined as theangular frequency for which the storage modulus, G′ equals the lossmodulus, G″.

REFERENCES

-   [1] Rheological characterization of polyethylene fractions”    Heino, E. L., Lehtinen, A., Tanner J., Seppala, J., Neste Oy,    Porvoo, Finland, Theor. Appl. Rheol., Proc. Int. Congr. Rheol, 11th    (1992), 1, 360-362-   [2] The influence of molecular structure on some rheological    properties of polyethylene”, Heino, E. L., Borealis Polymers Oy,    Porvoo, Finland, Annual Transactions of the Nordic Rheology Society,    1995.).-   [3] Definition of terms relating to the non-ultimate mechanical    properties of polymers, Pure & Appl. Chem., Vol. 70, No. 3, pp.    701-754, 1998.

2. Examples a) Preparation of the Catalyst

First, 0.1 mol of MgCl₂×3 EtOH was suspended under inert conditions in250 m1 of decane in a reactor at atmospheric pressure. The solution wascooled to the temperature of −15° C. and 300 m1 of cold TiCl₄ was addedwhile maintaining the temperature at said level. Then, the temperatureof the slurry was increased slowly to 20° C. At this temperature, 0.02mol of diethylhexylphthalate (DOP) was added to the slurry. After theaddition of the phthalate, the temperature was raised to 135° C. during90 minutes and the slurry was allowed to stand for 60 minutes. Then,another 300 ml of TiCl₄ was added and the temperature was kept at 135°C. for 120 minutes. After this, the catalyst was filtered from theliquid and washed six times with 300 ml heptane at 80° C. Then, thesolid catalyst component was filtered and dried. Catalyst and itspreparation concept is described in general e.g. in patent publicationsEP 491 566, EP 591 224 and EP 586 390.

For the preparation of Examples Ex1, Ex2, Ex3 and Ex4 as well asReference Example Ref5 triethylaluminium (TEAL),dicyclopentyldimethoxysilane (DCPDMS) as donor (Do), and the catalyst asproduced above were added into oil, like mineral oil, e.g. Technol 68(kinematic viscosity at 40° C. 62-74 cSt), in amounts so that Al/Ti was3-4 mol/mol, and Al/Do was as well 3-4 mol/mol. Catalyst concentrationin the final oil-catalyst slurry was 10-20 wt-%.

b) Polymerization of Examples Ex1-Ex4 and Reference Example Ref5

For the polymerization of Examples Ex1-Ex4 and Reference Example Ref5the catalyst was fed together with propylene to a prepolymerizationreactor. Triethylaluminium was used as a cocatalyst anddicyclopentyldimethoxysilane as a donor. The polymerization conditionsand feeds are listed in Table 1.

The slurry from the prepolymerization stage was directly fed to a loopreactor. Propylene, hydrogen and ethylene were further added to the loopreactor. The polymerization conditions and feeds are listed in Table 1.

The slurry from loop reactor was introduced to a gas phase reactor viadirect feed line, i.e. without monomer flashing in-between the reactors.Propylene, ethylene and hydrogen were fed to the gas phase reactor. Thepolymerization conditions and feeds are listed in Table 1.

In Examples Ex1 to Ex4 the low molecular weight fraction of thepropylene random copolymer is polymerized in the loop reactor whereasthe high molecular weight fraction of the propylene random copolymer ispolymerized in the subsequent gas phase reactor in the presence of thelow molecular weight fraction.

In Reference Example Ref5 the high molecular weight fraction of thepropylene random copolymer is polymerized in the loop reactor whereasthe low molecular weight fraction of the propylene random copolymer ispolymerized in the subsequent gas phase reactor.

a) Compounding and Pipe Extrusion

The polypropylene resins of Examples Ex1 to Ex4 and Reference ExampleRef5 emerging from the gas phase reactor (identified as reactor powderin Table 1) were compounded together with conventional antioxidants andCa-stearate (same amounts were used for Examples Ex1 to Ex4 andReference Example Ref5) and pelletized in a W&P ZSK 70 twin-screwextruder (Coperion) at a melt temperature of 240° C. and an extruderthroughput of 200 kg/h.

The polymer pellets of Examples Ex1 to Ex4 and Reference Example Ref5were prepared to test specimens for the mechanical and thermal tests aslisted below in Table 2 or were extruded to pipes in order to test theprocessability of the compositions.

TABLE 1 Polymerization conditions of Examples Ex1-4 and ReferenceExample Ref5 Ex1 Ex2 Ex3 Ex4 Ref5 Prepolymerisation step Cocatalyst(TEAL) feed 200 200 200 200 200 [g/t C3] Donor (DCPDMS) feed 30 30 30 3040 [g/t C3] Temperature [° C.] 30 30 30 30 30 Pressure [kPa] 5300 53005300 5300 5300 Loop Reactor Temperature [° C.] 70 70 70 70 70 Pressure[kPa] 5300 5300 5300 5300 5300 H2/C3 [mol/kmol] 0.61 0.62 0.65 0.5 0.07C2 content [wt-% 3.0 3.0 4.0 3.0 4.3 (mol %)] (4.4) (4.4) (5.9) (4.4)(6.3) MFR2 [g/10 min] 0.75 0.75 0.75 0.5 0.1 XCS [wt %] 5.0 5.0 7.0 5.07.7 Split [%] 40 40 40 40 60 Gas Phase Reactor Temperature [° C.] 80 8080 80 85 Pressure [kPa] 1600 1600 1600 1600 1600 H2/C3 [mol/kmol] 1.52.0 1.8 1.3 26 C2 content (calc.) 4.7 5.5 4.8 5.5 3.4 [mol %]* XCS [wt%](calc.)* 7.2 10.0 7.5 10.0 2.8 Split 60 60 60 60 40 Finalpolypropylene composition** C2 content [wt-% 4.0 4.5 4.5 4.5 4.0 (mol%)] (measured) (5.9) (6.6) (6.6) (6.6) (5.9) MFR₂ [g/10 min] 0.24 0.290.27 0.22 0.22 XCS [wt %] (measured) 6.3 8.0 7.3 8.0 5.8 C2 contentrefers to the ethylene comonomer content; C3 refer to the propylenemonomer feed. *calculated for the polymer polymerised in the gpr reactor(high molecular weight fraction) **measured from final polypropylenecomposition after the compounding step (a) as described above

TABLE 2 Mechanical and thermal properties of Examples Ex1 to Ex4 andReference Example Ref5 Ex1 Ex2 Ex3 Ex4 Ref5 MFR₂ (pellets) 0.24 0.290.27 0.22 0.22 [g/10 min] Flexural modulus [MPa] 935 811 854 783 964Charpy NIS, 23° C. 62.4 69.7 52.1 75.9 24.3 [kJ/m²] Charpy NIS, 0° C.6.9 11.8 6.5 9.6 3.6 [kJ/m²] Ten. Stress (yield) [MPa] 26.2 24.5 24.823.5 28.8 Ten. Strain (yield) [%] 12.8 12.9 12.9 14.0 12.7 PI 3.5 3.33.3 3.1 4.1

It can be seen from the results of Tables 2 and 3 that the Examples Ex1to Ex4 according to the invention show an improved balance of propertiesin terms of flexural modulus, Charpy notched impact strength at roomtemperature (23° C.) and cold temperature (0° C.), tensile stress atyield and tensile strain at yield.

By comparing the properties of the examples according to the inventionit can be seen that Examples Ex2 and Ex4 which have a higher amount ofethylene comonomer in the HMW fraction show a better impact performanceespecially at cold temperatures but also at room temperature compared toExamples Ex1 and Ex3.

Pipe Tests:

Test Pipe preparation: The polymers of Inventive Examples were extrudedto pipes by using a Reifenhauser 381-1-70-30 pipe extruder. Output ofthe extruder was 46 to 48 kg/h, melt pressure was 180 to 220 barg andthe melt temperature was 180 to 230° C. The test pipes had a diameter of32.3 mm and wall thickness of 3 mm. The shrinkage of the produced testpipes was clearly less than 5%.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.(canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)16. (canceled)
 17. A polypropylene composition suitable for pipeapplications comprising a propylene random copolymer with at least onecomonomer selected from alpha-olefins with 2 or 4 to 8 carbon atomswherein the polypropylene composition has a melt flow rate MFR₂ (2.16kg, 230° C.) of 0.05 to 1.0 g/10 min, determined according to ISO 1133,a polydispersity index (PI) of 2.0 to 7.0, and a Charpy Notched ImpactStrength at 0° C. of more than 4.0 kJ/m², determined according to ISO179/1eA:2000 using notched injection moulded specimens.
 18. Thepolypropylene composition according to claim 17, wherein the propylenerandom copolymer does not contain an elastomeric polymer phase dispersedtherein.
 19. The polypropylene composition according to claim 17,wherein the polypropylene composition has a flexural modulus of at least700 MPa, preferably at least 750 MPa, most preferably at least 780 MPato an upper limit of not more than 1200 MPa, determined according to ISO178 at a test speed of 2 mm/min and a force of 100N on test specimenshaving a dimension of 80×10×4.0 mm³ (length×width×thickness) prepared byinjection moulding according to EN ISO 1873-2.′
 20. The polypropylenecomposition according to claim 17, wherein the polypropylene compositionhas a tensile stress at yield of at least 15 MPa, preferably at least 20MPa, determined according to ISO 527-2:1996 using type 1A injectionmoulded test specimens prepared according to ISO 527-2:1996.
 21. Thepolypropylene composition according to claim 17, wherein thepolypropylene composition has a Charpy Notched Impact Strength at 23° C.of at least 30 kJ/m², preferably of at least 40 kJ/m², most preferablyof at least 45 kJ/m², determined according to ISO 179/1eA:2000 usingnotched injection moulded specimens.
 22. The polypropylene compositionaccording to claim 17, wherein the polypropylene composition has a meltflow rate MFR₂ (2.16 kg, 230° C.) of from 0.1 to 0.7 g/10 min,preferably of from 0.15 to 0.50 g/10 min, most preferably of from 0.2 to0.4 g/10 min, determined according to ISO
 1133. 23. The polypropylenecomposition according to claim 17, wherein the polypropylene compositionhas a polydispersity index (PI) of from 2.0 to 7.0, preferably from 2.0to 6.0, more preferably of from 2.5 to 5.0.
 24. The polypropylenecomposition according to claim 17, wherein the polypropylene compositionhas a content of xylene cold solubles (XCS) of from 1.0 to 15.0 wt %,preferably of from 2.0 to 12.0 wt %, most preferably of from 4.0 to 10.0wt %, determined at 25° C. according to ISO
 16152. 25. The polypropylenecomposition according to claim 17, wherein the propylene randomcopolymer is a propylene random copolymer with ethylene comonomer. 26.The polypropylene composition according to claim 17, wherein thecomonomer content of the propylene random copolymer is in the range of4.5 to 9.5 mol %, preferably 5.0 to 9.0, based on the total content ofmonomeric units in the propylene random copolymer.
 27. The polypropylenecomposition according to claim 17, wherein propylene random copolymercomprises at least a propylene random copolymer having a low molecularweight (low molecular weight (LMW) fraction) and a propylene randomcopolymer having a high molecular weight (high molecular weight (HMW)fraction), wherein the weight average molecular weight of the lowmolecular weight fraction is lower than that of the high molecularweight fraction, preferably wherein the propylene random copolymercomprises at least a propylene random copolymer having a low molecularweight (low molecular weight (LMW) fraction) and a propylene randomcopolymer having a high molecular weight (high molecular weight (HMW)fraction) and a higher content of comonomer, preferably ethylenecomonomer, than the propylene random copolymer having a low molecularweight fraction (LMW fraction), whereby the comonomer, preferablyethylene, content of LMW fraction is preferably 1.0 to 6.0 mol %,preferably 2.0 to 5.5 mol %, more preferably 3.0 to 5.0 mol %, based onthe total content of monomeric units in the LMW fraction.
 28. Thepolypropylene composition according to claim 17, wherein the lowmolecular weight fraction is present in the propylene random copolymerin an amount of 35 to 55 wt %, more preferably in an amount of 40 to 50wt % and most preferably in an amount of 40 to 47 wt %, based on thetotal amount of the propylene random copolymer (100 wt %), preferably,and the high molecular weight fraction is present in the propylenerandom copolymer in an amount of 65 to 45 wt %, more preferably in anamount of 60 to 50 wt % and most preferably in an amount of 60 to 53 wt%, based on the total amount of the propylene random copolymer (100 wt%).
 29. The polypropylene composition according to claim 17, wherein thepolypropylene composition does not comprise a polymeric nucleatingagent.
 30. A process for producing a polypropylene composition accordingto claim 17, wherein the propylene random copolymer is polymerized in amultistage polymerization process in the presence of (I) a solidcatalyst component comprising a magnesium halide, a titanium halide andan internal electron donor; and (II) a cocatalyst comprising analuminium alkyl and optionally an external electron donor, themultistage process comprising the steps of (a) continuously polymerizingpropylene together with a comonomer selected from alpha-olefins with 2or 4 to 8 carbon atoms, in a first polymerization stage by introducingstreams of propylene, hydrogen and said comonomer into the firstpolymerization stage at a temperature of 60 to 80° C. and a pressure of3000 to 6500 kPa to produce a first propylene random copolymer, whereinsaid first propylene random copolymer has a melt flow rate MFR₂ (2.16kg; 230° C.; ISO 1133) of from 0.2 to 3.0 g/min; (b) withdrawing fromthe first polymerization stage a stream comprising said first propylenerandom copolymer and transferring said stream into a secondpolymerization stage; (c) polymerizing propylene together with acomonomer selected from alpha-olefins with 2 or 4 to 8 carbon atoms, insaid second polymerization stage by introducing streams of propylene,said comonomer and optionally hydrogen into said second polymerizationstage at a temperature of 70 to 90° C. and a pressure of 1000 to 3000kPa to produce a propylene random copolymer of said first propylenerandom copolymer and a second propylene random copolymer; (d)continuously withdrawing a stream comprising said propylene randomcopolymer from the second polymerization stage and optionally mixingsaid propylene random copolymer with additives; and (e) extruding saidpropylene random copolymer mixture into pellets, which have a melt flowrate MFR₂ (2.16 kg; 230° C.; ISO 1133) of from 0.05 to 1.0 g/min, andwherein the first propylene random copolymer has preferably a higherMFR₂ than the second propylene random copolymer.
 31. A polypropylenecomposition according to claim 17 obtainable by the process wherein thepropylene random copolymer is polymerized in a multistage polymerizationprocess in the presence of (I) a solid catalyst component comprising amagnesium halide, a titanium halide and an internal electron donor; and(II) a cocatalyst comprising an aluminium alkyl and optionally anexternal electron donor, the multistage process comprising the steps of(a) continuously polymerizing propylene together with a comonomerselected from alpha-olefins with 2 or 4 to 8 carbon atoms, in a firstpolymerization stage by introducing streams of propylene, hydrogen andsaid comonomer into the first polymerization stage at a temperature of60 to 80° C. and a pressure of 3000 to 6500 kPa to produce a firstpropylene random copolymer, wherein said first propylene randomcopolymer has a melt flow rate MFR2 (2.16 kg; 230° C.; ISO 1133) of from0.2 to 3.0 g/min; (b) withdrawing from the first polymerization stage astream comprising said first propylene random copolymer and transferringsaid stream into a second polymerization stage; (c) polymerizingpropylene together with a comonomer selected from alpha-olefins with 2or 4 to 8 carbon atoms, in said second polymerization stage byintroducing streams of propylene, said comonomer and optionally hydrogeninto said second polymerization stage at a temperature of 70 to 90° C.and a pressure of 1000 to 3000 kPa to produce a propylene randomcopolymer of said first propylene random copolymer and a secondpropylene random copolymer; (d) continuously withdrawing a streamcomprising said propylene random copolymer from the secondpolymerization stage and optionally mixing said propylene randomcopolymer with additives; and (e) extruding said propylene randomcopolymer mixture into pellets, which have a melt flow rate MFR2 (2.16kg; 230° C.; ISO 1133) of from 0.05 to 1.0 g/min, and wherein the firstpropylene random copolymer has preferably a higher MFR₂ than the secondpropylene random copolymer.
 32. An article, preferably a pressure pipe,more preferably a hot and cold water pressure pipe, and/or fitting,comprising the polypropylene composition according to claim
 17. 33. Anarticle, preferably a pressure pipe, more preferably a hot and coldwater pressure pipe, and/or fitting, comprising the polypropylenecomposition according to claim 31.